Hydraulic percussion device and method of controlling same

Abstract

A hydraulic percussion device comprises a housing defining a longitudinal cylinder, a piston longitudinally reciprocal in the cylinder and subdividing same into a front compartment and a rear compartment, and a tool engageable longitudinally with the piston at the front compartment. The compartments are alternately and oppositely hydraulically pressurized to move the piston forward to strike the tool while traveling at an end speed and to move the piston backward away from the tool, the rate of alternation being a frequency parameter and the speed being a force parameter. A controller varies at least one of the parameters by detecting how much the piston rebounds from the tool after striking same and operating the control means in accordance with how much rebound is detected. How much the piston rebounds can be detected by sensing the pressure in one of the compartments immediately after the piston strikes the tool. As rebound increases the pressure in the rear compartment increases relative to a set point or pressure in the front compartment decreases relative to a set point, and vice versa. Rebound can also be detected by sensing the pressure in one of the compartments and at one of the sides of the source and operating the control means in accordance with the differential between these sensed pressures.

I claim: 
     
       1. A method of operating a hydraulic percussion device comprising: a housing defining a longitudinal cylinder;   a piston longitudinally reciprocal in the cylinder and subdividing same into a front compartment and a rear compartment;   a tool engageable longitudinally with the piston at the front compartment;   means for alternately and oppositely hydraulically pressurizing the compartments from a source having a high-pressure side and a low-pressure side to move the piston forward to strike the tool while traveling at an end speed and to move the piston backward away from the tool, the rate of alternation being a frequency parameter and the speed being a force parameter; and   control means for varying at least one of the parameters; the method comprising the steps of:   detecting how much the piston rebounds from the tool after striking same by sensing the pressure in one of the compartments immediately after the piston strikes the tool; and   operating the control means in accordance with how much rebound is detected.   
     
     
       2. The method defined in claim 1 wherein how much the piston rebounds is detected by sensing the pressure in one of the compartments and at one of the sides and operating the control means in accordance with the differential between these sensed pressures. 
     
     
       3. The method defined in claim 2 wherein the control means increases the pressure differential across the piston when moving forward when the pressure differential between the one compartment and the one side immediately after it strikes the tool increases and vice versa. 
     
     
       4. The method defined in claim 2 wherein the control means increases the length of the effective stroke of the piston when moving forward when the pressure differential between the one compartment and the one side immediately after it strikes the tool increases and vice versa. 
     
     
       5. A hydraulic percussion device powered by a hydraulic source having a high-pressure side and a low-pressure side, the device comprising: a housing defining longitudinal main cylinder;   a piston longitudinally reciprocal in the main cylinder and subdividing same into a front compartment and a rear compartment;   a tool engageable longitudinally with the piston at the front compartment;   means for alternately and oppositely hydraulically pressurizing the compartments to move the piston forward to strike the tool while traveling at an end speed and to move the piston backward away from the tool, the rate of alternation being a frequency parameter and the speed being a force parameter;   control means for varying at least one of the parameters;   means for detecting how much the piston rebounds from the tool after striking same including means for sensing the pressure in one of the compartments immediately after the piston strikes the tool; and   means for operating the control means in accordance with how much rebound is detected.   
     
     
       6. A hydraulic percussion device powered by a hydraulic source having a high-pressure side and a low-pressure side, the device comprising: a housing defining a longitudinal main cylinder;   a piston longitudinally reciprocal in the main cylinder and subdividing same into a front compartment and a rear compartment;   a tool engageable longitudinally with the piston at the front compartment;   means for alternately and oppositely hydraulically pressurizing the compartments to move the piston forward to strike the tool while traveling at an end speed and to move the piston backward away from the tool, the rate of alternation being a frequency parameter and the speed being a force parameter;   control means for varying at least one of the parameters;   means for detecting how much the piston rebounds from the tool after striking same;   means for operating the control means in accordance with how much rebound is detected, said control means including: a control valve connected to both sides of the source and to the rear compartment; and   a buffer valve connected between the control valve and the front compartment, the detecting means including a detecting valve connected to the source and to the buffer valve.     
     
     
       7. The device defined in claim 6 wherein the detecting valve is a sequencing valve connected between the rear compartment, the high-pressure side, and the buffer valve. 
     
     
       8. The device defined in claim 6 wherein the detecting valve is a sequencing valve connected between the front compartment, the high-pressure side, and the buffer valve. 
     
     
       9. The device defined in claim 6 wherein the detecting valve is a check valve connected between the rear compartment and the buffer valve. 
     
     
       10. The device defined in claim 6 wherein the buffer valve has: a cylinder,   a slide subdividing this buffer-valve cylinder into a a chamber connected to the detecting valve and a chamber connected to one side of the source,   a restriction through which flow between the chambers is possible,   a spring urging the slide to decrease the volume of one of the chambers and increase the volume of the other chamber.   
     
     
       11. The device defined in claim 10 wherein the one side is the low-pressure side and the one chamber is the chamber connected to the detecting valve, the detecting valve being a pressure-threshold valve connected between the high-pressure side of the source and the rear compartment and operable to connect the detecting-valve chamber of the buffer valve to the high-pressure side when the pressure in the rear compartment exceeds the pressure of the high-pressure side, the high-pressure side being directly connected to the front compartment. 
     
     
       12. The device defined in claim 10 wherein the slide is formed with an outwardly open groove, the control valve being connected via a passage continuously to this groove, the device further having a plurality of ducts opening into the main cylinder at spaced locations and into the buffer-valve cylinder at corresponding spaced locations, the groove successively exposing the ducts on expansion of the other compartment. 
     
     
       13. The device defined in claim 12 wherein the one side is the low-pressure side and the detecting valve is connected between the rear compartment and the high-pressure side and is operable to open when the pressure in the rear compartment exceeds that at the high-pressure side. 
     
     
       14. The device defined in claim 12 wherein the one side is the high-pressure side and the detecting valve is connected to the front compartment. 
     
     
       15. A hydraulic percussion device powered by a hydraulic source having a high-pressure side and a low-pressure side, the device comprising: a housing defining a longitudinal main cylinder;   a piston longitudinally reciprocal in the main cylinder and subdividing same into a front compartment and a rear compartment;   a tool engageable longitudinally with the piston at the front compartment;   means for alternately and oppositely hydraulically pressurizing the compartments to move the piston forward to strike the tool while traveling at an end speed and to move the piston backward away from the tool, the rate of alternation being a frequency parameter and the speed being a force parameter;   control means for varying at least one of the parameters;   means for detecting how much the piston rebounds from the tool after striking same including means for sensing the pressure in one of the compartments and at one of the sides and operating the control means in accordance with the differential between these sensed pressures; and   means for operating the control means in accordance with how much rebound is detected.   
     
     
       16. The device defined in claim 15 wherein the control means increases the pressure differential across the piston when moving forward when the pressure differential between the one compartment and the one side immediately after it strikes the tool increases and vice versa. 
     
     
       17. The device defined in claim 15 wherein the control means increases the length of the effective stroke of the piston when moving forward when the pressure differential between the one compartment and the one side immediately after it strikes the tool increases and vice versa.